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Green synthesis of 2,3,4,9-tetrahydro-1H-carbazoles/ 2,3-dimethylindoles catalyzed by [bmim (BF 4)] ionic liquid in methanol

Tamatakallu O. Shrungesh Kumar and Kittappa M. Mahadevan

Department of Post Graduate Studies and Research in Chemistry, School of Chemical Science, Kuvempu University, Shankaraghatta, Karnataka, 577451, India

Abstract: 1-butyl-3-methylimidazolium tetrafluoroborate [bmim (BF 4)] ionic liquid has been used as catalyst for the synthesis of tetrahydrocarbazoles and 2, 3-dimethylindoles with excellent yields in a shorter reaction time. The results show that the [bmim (BF 4)] ionic liquid is very efficient in the Fischer indole synthesis due to its operational simplicity, high yields, dual catalyst-solvent properties and reused for five consecutive reactions without significant loss of catalytic efficiency. The applicability of the methodology for large-scale reaction highlights its potentiality for industrial scale synthesis. The main advantage of this procedure is that the products could be obtained in pure form after filtration and evaporation of MeOH solvent.

Keywords: Fischer indole synthesis; 2,3,4,9-tetrahydro-1H-carbazoles; 2, 3-dimethylindoles; 1-butyl-3-methylimidazolium tetrafluoroborate; ionic liquid.